Zener Diodes
Understanding & Using Solar DC-AC Inverters – Part 2
Understanding & Using Solar DC-AC Inverters – Part 2
Output regulation
We take for granted the fact that our mains power is very well regulated . so
you can plug almost any appliance into a standard point outlet, and it will
operate correctly. That.s because the electricity supplier has enormous generating
plants, with automatic regulation systems to keep the mains voltage and
frequency very close to constant, despite load variations of many megawatts.
Inevitably you can.t get this kind of performance from a much smaller electronic
inverter, connected to a modest battery or solar panel as the energy source.
However most modern inverters can provide reasonably good regulation for loads
of up to their rated capacity (given in watts) . assuming of course that they.re
running from a well-charged battery.
In this type of inverter it isn.t feasible to control the peak-to-peak output,
because this is largely fixed by the battery voltage and the transformer.s step-up
ratio. So in most cases the regulation is achieved in a different way: by varying
the width of the rectangular pulses, to control the .form factor. and hence the
RMS value of the output voltage.
This is called pulse width modulation (PWM), and is usually done by having a
feedback system which senses the inverter.s output voltage (or load current).
When this feedback senses that the load on the inverter.s output has increased,
the inverter.s control circuitry acts to increase the width of the pulses which turn
on the MOSFETs. So the MOSFETs turn on for longer each half-cycle,
automatically correcting the RMS value of the output to compensate for any
droop in peak-to-peak output.
The resulting regulation is usually capable of keeping the RMS value close to
constant, for loads up to the inverter.s full rated output power. However this
approach does have limitations, mainly because it can generally only increase the pulse width to a certain point. (In the extreme, the output becomes a square wave.) This may not be sufficient to allow the inverter to deliver enough RMS output voltage
in short-term overload or .surge. conditions. When many types of appliance are first turned on, for example, they draw a .startup. current which is many times greater than the current drawn when they.re running. This type of surge can overload the inverter, and its protection circuitry may .shut it down. To prevent damage to the transformer and MOSFETs.
Some types of inverter incorporate special .soft start. circuitry, to allow the inverter to cope with this type of short load current surge. The output voltage and power may drop, but at least the inverter keeps operating and allows the appliance to start up.
Even so, there are some appliances and tools that are simply not compatible with inverters, because of their tendency to draw an extremely high startup current.
Examples are refrigerators, freezers, air conditioners or any other appliance where a motor is driving a compressor or pump. As the motor in these appliances often has a very heavy load right at switch-on (with the compressor near .top dead centre.), it can need to draw a huge current simply in order to start rotating.
This type of appliance and tool should really be powered using a suitably rated engine-driven alternator, not a DC-AC inverter.
Voltage spikes
Another complication of the fairly high harmonic content in the output of
.modified sinewave. inverters is that appliances and tools with a fairly inductive
load impedance can develop fairly high voltage spikes due to inductive .back
EMF.. These spikes can be transformed back into the primary of the inverter.s
transformer, where they have the potential to damage the MOSFETs and their
driving circuitry.
The risk of damage is fairly small during the actual power pulses of each cycle,
because at these times one end of the primary is effectively earthed. Transformer
action thus prevents the .other. end from rising higher than about twice the
battery voltage.
However as you can see from Fig.2, there are times during every
cycle of operation when neither of the switching MOSFETs is conducting: the
.flats. between the rectangular pulses. It.s at these times that the spikes can
produce excessive voltage across the MOSFETs, and potentially cause damage.
It.s for this reason that many inverters have a pair of high-power zener diodes
connected across the MOSFETs, as shown in Fig.1.
The zeners conduct heavily as soon as the voltage rises excessively, protecting the MOSFETs from damage.
Another approach is to have high-power standard diodes connected from each
end of the primary to a large electrolytic capacitor, which becomes charged up to
twice the battery voltage. When the ends of the primary attempt to rise higher
than this voltage, the diodes conduct and allow the capacitor to absorb the spike
energy.
Thanks to this type of protection, most inverters are fairly tolerant of moderately
inductive loads. However they may not be able to cope with heavy loads that are
also strongly inductive . like heavy duty tools and machinery, or more than
one or two fluorescent lights.
Quite apart from the generation of voltage spikes, heavily inductive loads tend
to demand current which is strongly shifted in phase relative to the inverter.s
output voltage pulses. This makes it hard for the inverter to cope, because the
only energy available to the load between the pulses is that stored in the
transformer.
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300 Micro Semi 1N5270B 91V Zener Diodes $19.99 |
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Lot of (100) Diodes Inc MMBZ5248B-7-F Diode Zener 18V 350MW SOT23-3 $7.50 |
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NEW 1N4731A 4.3V 1W DO-41 GLASS 5% 10 X Zener Diode $0.01 |
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NEW 1/2W 0.5W Zener Diode 30 Value Assorted 2v ~ 39v Kit Qty 300pcs $8.20 |
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500 MELF SMT 15V 500mA Zener Diodes $12.99 |
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new 1/2w 0.5w Watt 2v ~ 39v Zener Diode 30 Value Assorted Qty 300pcs $8.20 |
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100x Zener Diode 5.1V/0.5W 1N5231B 1N5231 $3.53 |
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100 pcs 33V Zener Diode 0.5W 500mW 1/2W DO35 RoHS $1.50 |
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NEW 1N5364B 1N5364 ZENER DIODE 5 PIECES $1.00 |
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10 X Zener Diode 1N4754A 39V 1W DO-41 GLASS 5% [EZD27] $0.01 |
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11V 1W DO-41 GLASS 5% 10 X Zener Diode 1N4741A NEW $0.01 |
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new 30V 1W DO-41 GLASS 5% 10 X Zener Diode 1N4751A $0.01 |
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1 Lot of 250 Zener Diode 1N5362A. New parts $24.99 |
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10 X Zener GLASS Diode Rectifier 1N4755A 43V 1W DO-41 $0.01 |
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500 Pcs 1/2W DIP Voltage Regulators Axial Zener Diodes $14.97 |
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10 X Zener Diode 1N4752A 33V 1W DO-41 GLASS 5% [EZD25] $0.01 |
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24 pcs 1N5368BG 47V, 5W ZENER DIODE 1N5368 by On Semi, Lead Free $7.95 |
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24 pcs 1N5341BG 6.2V, 5W ZENER DIODE 1N5341 by On Semi, Lead Free $7.95 |
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APPRX 500PC 1N4732A 4.7VOLT 1WATT ZENER DIODE LOT $9.95 |
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24 pcs 1N5342BG 6.8V, 5W ZENER DIODE 1N5342 by On Semi, Lead Free $7.95 |
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24 pcs 1N5384BG 160V, 5W ZENER DIODE 1N5384 by On Semi, Lead Free $7.95 |
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24 pcs 1N5352BG 15V, 5W ZENER DIODE 1N5352 by On Semi, Lead Free $7.95 |
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8.2V 1/2W Glass Sealed Package DIP Zener Diodes 100 Pcs $6.11 |
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24 pcs 1N5355BG 18V, 5W ZENER DIODE 1N5355 by On Semi, Lead Free $7.95 |
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24 pcs 1N5346BG 9.1V, 5W ZENER DIODE 1N5346 by On Semi, Lead Free $7.95 |
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24 pcs 1N5349BG 12V, 5W ZENER DIODE 1N5349 by On Semi, Lead Free $7.95 |
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1N5314 GLASS ZENER DIODE TIN NOS $4.95 |
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1N5308 KSI ZENER DIODE NOS $4.95 |
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1N5318 SI GLASS ZENER DIODE NOS $3.95 |
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10 X Zener Diode 1N4757A 51V 1W DO-41 GLASS 5% [EZD30] $0.01 |
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NEW 1N4735A 6.2V 1W DO-41 GLASS 5% 10 X Zener Diode $0.01 |
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1/2W Through Hole Zener Diodes Voltage Regulators 4B1 $12.60 |
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Tympanium Zener Diode Rectifier BSA Lightning Thunderbolt Norton Atlas Victor $49.99 |
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ZENER DIODE 1WATT JAN1N3038B “d” GOLD 1970 1N3038B $19.95 |
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8pk – 1N4736 (6.8V) Zener Diodes $1.00 |
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8pk – 1N5225B – 3V – Zener Diode $1.00 |
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ZENER DIODE 1WATT JAN1N3038B CCZL GOLD 1968 1N3038B $29.95 |
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ZENER DIODE 1N3073 VINTAGE GOLD 1962 $29.95 |
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ZENER DIODE 1N3073 VINTAGE TIN 1967 $19.95 |
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1N2831B-JANTX (MIL SPEC) ZENER DIODE 51v,50w (LOT OF 4) $33.00 |
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1N5232B ZENER DIODE 5.6V 1/2W MOTOROLA X 40 Pcs. $3.49 |
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Microtron IN5257B,1/2W, 5%, 33V, zener diodes, REEL $161.95 |
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100x Zener Diode 4.7V/0.5W 1N5230B 1N5230 $3.53 |
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10 – NTE140A 10V/ 1Watt Zener Diode – NEW $5.00 |
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2200 Temic TZM5240B MiniMelf Small Signal Zener Diodes $24.99 |
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ZENER DIODE 1N3037B ETCO GOLD Vintage 1N3037 $19.95 |
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ZENER DIODE 1N3037 SEMCOR TIN Vintage 1N3037 $14.95 |
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BZX55-C24 DIODE, ZENER 24V, 500mW…Pack of 100 $6.60 |
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BZX55-C5V1 DIODE, ZENER 5V1, 500mW…Pack of 100 $6.60 |
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3K NXP BZX284-C5V1 5.1V zener diode SOD110 SMT 7″ reel $60.00 |
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10pk – 1N4372 Zener Diodes $1.00 |
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10pk – 12V- .4W Zener Diodes # 1N963 $1.00 |
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10 X Zener Diode 1N4756A 47V 1W DO-41 GLASS 5% [EZD29] $0.01 |
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NEW 1N4749A 24V 1W DO-41 GLASS 5% 10 X Zener Diode $0.01 |
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10 X Zener Diode 1N4732A 4.7V 1W DO-41 GLASS 5% [EZD05] $0.01 |
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300 X 1N4728 – 1N4728A 3.3V 1 WATT ZENER DIODE DO-41 GLASS ON TAPE 300 PCS $13.45 |
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1N4763 /ECG5095A 1W ZENER DIODE $2.95 |
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500 Pcs 1/2W 5.1V DIP Voltage Regulators Zener Diodes $14.96 |
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50x Zener Diode 5.1V/1W 1N4733A 1N4733 $3.51 |
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D817A USSR Powerful Zener Diodes Lot of 12 NOS $5.00 |
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D817B USSR High Voltage Zener Diodes Lot of 12 NOS $5.00 |
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D816G USSR High Voltage Zener Diodes Lot of 12 NOS $5.00 |
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20pk-1N5240 Zener Diodes $1.00 |
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16pk-1N5256B Zener Diodes $1.00 |
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2N3904 2N3906 PN2222A PN2907A 2N4401 2N4403 3.3V – 36V ZENER DIODE KIT 200X & MO $22.00 |
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2500 Pcs SMD SMT Zener Diode Voltage Regulator 2.4V 5mA $27.61 |
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1N4748A 22V 1W 5% ZENER DIODE 10ea lot free shipping $4.99 |
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1N4735A DIODE ZENER 6.2V 1W 5% DO-41 BULK (20pc) USA $0.99 |
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100x Zener Diode 12V/0.5W 1N5242B 1N5242 $3.53 |
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Diodes BZT52C5V1-7 Zener Diodes 5.1V 500mW SOD123 50pcs $3.25 |
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1/2W 2V-39V Zener Diode Assorted Kit 30valuesX10pcs $9.90 |
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1W 3.6V-43V Zener Diode Assorted Kit 24values 240pcs volatage regualtor $9.90 |
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10 pcs New Zener Diode Rectifier 1N4753A DO-41 GLASS 5% $0.01 |
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New 1W DO-41 GLASS 5% 10 X Zener Diode 1N4753A 36V $0.01 |
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DIP Zener Diodes 2.4V 1/2W for Liquid Crystal Display $6.69 |
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NEW 1N4747A 20V 1W DO-41 GLASS 5% 10 X Zener Diode $0.01 |
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100pcs, Zener Diode 12V/0.5W 1N5242B 1N5242,3322 $10.99 |
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100pcs, Zener Diode 24V/0.5W 1N5252B 1N5252,3323 $10.99 |
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100pcs, Zener Diode 5.6V/0.5W 1N5232B 1N5232,3321 $10.99 |
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20pcs, Zener Diode 12V/0.5W 1N5242B 1N5242,3322 $2.99 |
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20pcs, Zener Diode 5.6V/0.5W 1N5232B 1N5232,3321 $2.99 |
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50pcs, Zener Diode 12V/0.5W 1N5242B 1N5242,3322 $5.99 |